1. Field of the Invention
The present invention relates to a mold for manufacturing a multilayer molding and methods for manufacturing a multilayer molding.
2. Description of the Related Art
Multilayer moldings, partially laminated with a skin material covering a thermoplastic resin substrate, have been extensively used for automobile interior parts such as door trims, rear trims and instrument panels, as well as for consumer electronics.
The multilayer molding partially laminated with the skin material is generally manufactured by a compression molding method in which the skin material is placed in a specified position on a mold surface. Molten thermoplastic resin is then fed into the mold and the mold is pressurized and clamped until the cavity clearance achieves the final product thickness. Hereinafter, "thermoplastic resin" will be used interchangeably with "resin".
However, in such a method, it is difficult to accurately hold the skin material in the specified position on the mold surface. As a result of this placement difficulty, the skin material is displaced in the molding process by the feed pressure of the molten resin as well as by the flow of the molten resin in the molds at the time of clamping and the skin material will not be laminated in the specified position.
In an attempt to overcome these placement problems, Japanese Examined Patent Publication No. Hei 4-26289 proposed a method comprising steps of using a mold having bulkheads on a mold surface corresponding to the peripheral part of the skin material; allowing a fringing end of the skin material to lie along the bulkheads; locating the skin material inside an area surrounded by the bulkheads in a manner such that the skin material contacts the mold surface; optionally arresting the skin material fringing end on top of the bulkheads to fix the skin material if the top is sawtooth-like; and feeding molten resin.
In this method, the skin material is located inside the area surrounded by the bulkheads. However, because the skin material is not particularly fixed to the mold surface or because the arresting force is not sufficient even if the skin material fringing end is arrested at the sawtooth-like top of the bulkheads, the skin material moves over the bulkheads. The skin material moves over the bulkheads due to the feed pressure of the molten resin or the flow of the molten resin in the molds at the time of clamping. Therefore, it is difficult to accurately prevent displacement of the skin material with this method. Consequently, there is a problem with this method in that the skin material is limited to a thick fiber material which is less susceptible to the feed pressure of the molten resin or to the flow of the molten resin in the mold during mold clamping, or in that it is necessary to preform the skin material so that it may fit into the bulkheads.
Another method for the manufacture of a multilayer molding partially laminated with skin material is known where a multilayer molding having a part of the substrate surface laminated with a first skin material and the remaining part of the substrate surface laminated with a second skin material. Japanese Non-examined Patent Publication No. Hei 2-206513 discloses this method for the manufacture of a multilayer molding comprising the steps of inserting the fringing end of a first skin material into a circumferential groove provided on a mold surface; laying a second skin material on the overall surface of the mold surface while covering the first skin material with the second skin material; feeding a molten resin into a clearance between the skin material and the mold surface; and then cutting off a part of the second skin material overlapping the first skin material.
However, even in this process, because the first skin material fringing end is simply inserted into the circumferential groove, the first skin material is moved due to the feed pressure of the molten resin or the flow of the molten resin in the mold at the time of mold clamping. Therefore, it is difficult to accurately laminate the first skin material on the specified position of the substrate surface with this method.